Not Applicable
Not Applicable
1. Technical Field
This invention relates in general to electronic circuits and, more particularly, to digital to analog converters.
2. Description of the Related Art
Digital-to-analog converters (DACs) are used in many applications where data is processed in the digital domain and converted to the analog domain. A typical example of DAC use is in cellular telephones, where voice data is communicated digitally and converted to an analog signal to drive a speaker for output to the user. DACs are used in a wide range of applications in many different devices.
In many applications, minimizing the consumption of power is extremely important since the device is powered by a battery. For portable devices such as cellular phones and portable audio equipment, a major selling factor is the size and weight of the device. Accordingly, the size, and hence the capacity, of the battery used to power the device is diminishing, while the appeal of longer battery life and output quality are increasing.
Therefore, it is beneficial to use a highly efficient class-D amplifier stage in a DAC. Unfortunately, the modulation of the class-D amplifier stage by a pulse width modulation device (PWM) results in common mode noise generation. To compensate for the common mode noise, the prior art uses a feedback control system that requires conversion of the analog output of the class-D amplifier to a digital signal to be used in the PWM. This feedback system complicates the design and increases power requirements.
Therefore, a need has arisen for a more efficient digital to analog converter, without sacrificing output quality.
In the present invention, a digital to analog converter comprises an amplifier circuit and a pulse width modulator. The pulse width modulator generates signals on first and second nodes of amplifier circuit to create a differential signal. Compensation circuitry generates an identical signal on said first and second nodes to obtain a desired common mode average signal between said first and second nodes, such that said differential signal is not affected.
The present invention provides significant advantages over the prior art. First, the analog/ digital converter is no longer needed, because feedback is not necessary for the compensation. Thus, the circuit design is simplified and the power consumed by the analog/digital converter is eliminated. Second, the compensation signals do not affect the differential signal, resulting in a pure signal.